U.S. Pat. No. 4,647,576, which is herein incorporated by reference, discloses certain trans-6-[2-(substituted-pyrrol-1-yl)alkyl]-pyran-2-ones.
U.S. Pat. No. 4,681,893, which is herein incorporated by reference, discloses certain trans-6-[2-(3- or 4-carboxamido-substituted pyrrol-1-yl)alkyl]-4-hydroxy-pyran-2-ones.
The compounds disclosed in the above U.S. patents are useful as inhibitors of the enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA reductase) and are thus useful hypolipidemic and hypocholesterolemic agents. Particularly valuable as hypolipidemic and hypocholesterolemic agents are trans(.+-.) 5-(4-fluorophenyl)-2-(1-methylethyl)-N,4-diphenyl-1-[2-(tetrahydro-4-hydro xy-6-oxo-2H-pyran-2-yl)ethyl]-1H-pyrrole-3-carboxamide and (2R-trans)-5-(4-fluorophenyl)-2-(1-methylethyl)-N,4-diphenyl-1-[2-(tetrahy dro-4-hydroxy-6-oxo-2H-pyran-2-yl)ethyl]-1H-pyrrole-3-carboxamide. The aforementioned compounds have been prepared by a linear synthetic route which employed two reactions conducted at low temperatures (-78.degree. C.) under carefully controlled conditions. The two reactions included the addition of the dianion of ethyl acetoacetate to an aldehyde and the reduction of the hydroxy ketone produced in this reaction with sodium borohydride and a trialkylborane. Although these reactions provide the target compounds in high diastereomeric excess, they are difficult to conduct on large-scale and use expensive reagents which are difficult to handle. They also do not produce enantiomerically pure products. The materials produced by the earlier methods can be separated into enantiomerically pure products but the process is very expensive, time-consuming, and results in the loss of more than 50% of the starting material.
The object of the present invention is an improved process for preparing the compounds described above by using a novel synthesis.
Further, we have unexpectedly found that the particularly valuable hypolipidemic and hypocholesterolemic agents trans(.+-.)5-(4-fluorophenyl)-2-(1-methylethyl)-N,4-diphenyl-1-[2-(tetrahy dro-4-hydroxy-6-oxo-2H-pyran-2-yl)ethyl]-1H-pyrrole-3-carboxamide and (2R-trans)-5-(4-fluorophenyl)-2-(1-methylethyl)-N,4-diphenyl-1-[2-(tetrahy dro-4-hydroxy-6-oxo-2H-pyran-2-yl)ethyl]-1H-pyrrole-3-carboxamide can be prepared from a novel intermediate in fewer steps and higher yields than the previous methods. Moreover, the present method proceeds from inexpensive starting materials and is amenable to large-scale synthesis.